Dual loop signal quality based link adaptation

ABSTRACT

A communications link is adapted based on a quality estimate for a signal transmitted via the communications link. The method comprises receiving and demodulating the transmitted signal, assessing the demodulated signal to derive a first estimate for the signal quality that is to be used in a link adaptation scheme, and further processing and decoding the demodulated signal. Based on at least one of the further processed, non-decoded signal and information obtained prior to conclusion of decoding, a first control signal indicative of the signal quality is generated and utilized to control the link adaptation scheme.

This application is the US national phase of international applicationPCT/EP2003/002775 filed 17 Mar. 2003, which designated the U.S., theentire content of which is hereby incorporated by reference.

TECHNICAL FIELD

The technology relates to a method, a device and a system that areinvolved in a link adaptation mechanism. More specifically, thetechnology relates to adapting a communications link between atransmitter and a receiver based on a quality estimate for a signaltransmitted via the communications link.

BACKGROUND

Wireless cellular communications is continuing to grow unabated. Aswireless applications become increasingly widespread, the pressure onnetwork operators to increase the capacity of their networks becomesmore intense.

There are a number of ways of enhancing capacity in a wireless cellularnetwork, including frequency hopping, micro cells, the introduction ofadaptive antennas, and link adaptation. Link adaption has thus become anobject of increasing interest in recent years.

In the following, conventional link adaptation mechanisms will bedescribed for an exemplary wideband code division multiple access(WCDMA) scenario. A typical WCDMA scenario including two mobile devices(user equipment, UE), a base station (BS) communicating with the UEs,and a radio network controller (RNC) communicating with the BS is shownin FIG. 1. As can be seen from FIG. 1, WCDMA downlink transport channelsto the UEs include a dedicated channel (DCH) and a high-speed downlinkshared channel (HS-DSCH). The HS-DSCH is allocated to an UE on atime-slot by time-slot basis.

The basic link adaptation mechanisms in the WCDMA standard include powercontrol on the DCH and adaptive coding and modulation on the HS-DSCH.Power control on DCH avoids allocating more power than is actuallyrequired to achieve a certain decoding quality to individualcommunications links. Since the total transmit power of the BS islimited, the implementation of such a power control scheme increases thenetwork capacity. Additionally, avoiding excessively high power levelshelps to reduce signal interference.

According to the link adaptation mechanism of adaptive coding andmodulation, the transmission rate is adapted to the time-varying channeland interference conditions. In the case of favourable channelconditions for example, a larger modulation format or higher code rateis used to increase the data rate and thus enhance the network capacity.

A power control scheme in a WCDMA link adaptation context is for exampledescribed in H. Schotten and J. Röβler, “System Performance Gain inInterference Cancellation for WCDMA Dedicated and High-Speed DownlinkChannels”, VTC 2002, Vancouver. The UE receiver configuration requiredto implement such a power control based link adaptation mechanism isdepicted in FIG. 2 and will now be described in more detail.

A signal received from the BS by the UE receiver is demodulated, Rakecombined and subjected to an interference cancellation step. Based onthe signal that has been subjected to interference cancellation, anestimate for the signal-to-interference ratio (SIR) is determined andcompared to a SIR target value. Depending on the result of thiscomparison, a power control algorithm generates a power up or a powerdown command for downlink that is sent in the uplink to the BS. Thus, afast power control loop is established that allows adjustment of thepower once per slot (at a rate of 1500 slots per second).

In addition to this fast power control loop an outer power control loopis provided. The outer power control loop adjusts the target SIRsetpoint and aims at a constant frame error rate (FER). Outer loopcontrol is based on a check of the cyclic redundancy code (CRC) that isobtained during decoding of a particular data frame. If for example theCRC check indicates that the transmission quality is decreasing, the SIRtarget may be increased and vice versa.

As has been mentioned above, adaptive coding and modulation is a furtherexample of an efficient link adaptation mechanism. In FIG. 6, anapproach for adaptive coding and modulation on a HS-DSCH known from H.Schotten and J. Röβler, “System Performance Gain in InterferenceCancellation for WCDMA Dedicated and High-Speed Downlink Channels”, VTC2002, Vancouver is depicted. In the scenario of FIG. 6, the transmissionpower is kept constant but the transmission rate is adapted to thecurrent channel and interference conditions. A received signal that hasbeen demodulated, Rake combined and subjected to interferencecancellation is assessed to generate an estimate for the channelquality. This estimate is then used for channel quality indicator (CQI)signaling in uplink. The CQI signaling determines the modulation formatand code rate that is used on downlink. By varying the modulation formatand the code rate, the data rate on downlink can be adapted to thetime-varying channel and interference conditions.

Efficient link adaptation requires a sufficiently accurate estimation ofthe quality of the received signal on the one hand and, to closely trackchannel and interference conditions, a low estimation and reportingdelay of the signal quality on the other hand. These requirements arecontradictory because depending on the implementation details of thereceiver, a fast estimation of signal quality and a low reporting delaydo often not allow a sufficiently accurate signal quality estimation.

There is thus a need for a method, a device and a system that enable amore efficient link adaptation based on a signal quality estimate.

SUMMARY

The need for efficiently adapting a communications link between atransmitter and a receiver based on a quality estimate for a signaltransmitted via the communications link is satisfied by a linkadaptation approach comprising receiving and demodulating thetransmitted signal, assessing the demodulated signal to derive a firstestimate for the signal quality that is to be utilized in a linkadaptation scheme, and further processing and decoding the demodulatedsignal. Based on at least one of the further processed, non-decodedsignal and information obtained prior to conclusion of decoding, a firstcontrol signal indicative of the signal quality is generated andutilized to control the link adaptation scheme.

Control of the link adaptation scheme based on the first control signalprior to completion of the decoding operation allows an improved linkadaptation with respect to the tracking speed and tracking accuracy oftime-varying channel and interference conditions. Moreover, based on thefirst control signal, it is possible to implement signal qualityestimation as a two-step or multiple-step procedure. Thus signal qualityestimation becomes more robust.

The further processing that is performed between demodulation anddecoding preferably includes at least one of Rake combining,de-interleaving and advanced receiver techniques like interferencecancellation. It is particularly advantageous to derive the firstestimate for the signal quality from the demodulated signal prior tosubjecting the demodulated signal to an advanced receiver technique andto generate the first control signal generated on the basis of a signalthat has been subjected to an advanced receiver technique. Generation ofthe first estimate prior to performing an advanced receiver techniqueensures that an additional processing delay associated with the advancedreceiver technique does not result in a link adaptation delay.Additionally, controlling the link adaptation scheme with the firstcontrol signal after the advanced receiver technique has been performedallows (prior to conclusion of demodulation) the taking into account ofsignal enhancement effects that resulted from the advanced receivertechnique and that would not be or only with difficulty be predictableprior to applying the advanced receiver technique to the demodulatedsignal.

The first control signal may be generated on the basis of a secondestimate for the signal quality or may form the basis for generating thesecond estimate. The first estimate and the second estimate for thesignal quality are preferably derived from the demodulated signal atdifferent processing stages. This means that the demodulated signal fromwhich the second estimate is derived might have been processed furthercompared to the demodulated signal that formed the basis for derivingthe first estimate. Thus, the second estimate will in general be moreaccurate than the first estimate but will become available at a laterpoint in time. The second estimate, although more accurate, willtherefore be associated with a larger processing delay.

At least one of the first control signal and the second estimate may begenerated based on metrics information obtained during furtherprocessing or decoding. Thus, metrics information derived in thereceiver may be utilized to control the link adaptation scheme.

Various link adaptation schemes can be implemented. According to apreferred example, the link adaptation scheme includes an associationbetween the first estimate and an adaptation signal controlling thecounterpart of the receiver, i.e., the transmitter. Such an associationmay for example be defined by a mapping mechanism or any other mechanismthat allows generation of an adaptation signal from the first estimatein a replicable manner. The adaptation signal may for example be a powerup command, a power down command or a command that is used in contextwith CQI signalling.

If a link adaptation scheme defining an association between the firstestimate and an adaptation signal is implemented, the first controlsignal may be used to control (e.g. change) this association. If forexample a mapping mechanism between the first estimate and acorresponding adaptation signal is defined, the first control signal maybe used to adjust this mapping mechanism to thereby improve linkadaptation, e.g., improve at least one of transmit power control,adaptive coding and adaptive modulation.

The decoded signal or information like the CRC obtained as a decodingresult may be assessed to generate a second control signal for e.g.additionally controlling the link adaptation scheme or for triggeringre-transmission. The second control signal will however not be based onan estimate for the signal quality but on a “hard figure” like the CRCor on the decoded signal. The second control signal allowsimplementation of a two-step control of the link adaptation scheme,namely a faster but less accurate control step on the basis of the firstcontrol signal and a slower but more accurate control step on the basisof the second control signal.

According to a further aspect in context with the link adaptationschemes of adaptive coding, adaptive modulation or a combinationthereof, a first estimate for the signal quality that is to be utilizedin the particular link adaptation scheme is derived from the demodulatedsignal prior to decoding thereof. Based on the decoded signal or oninformation that has become available only after decoding (like theCRC), a control signal indicative of the signal quality may be generatedand utilized to control at least one of adaptive coding and adaptivemodulation. The first control signal is preferably generated on thebasis of an assessment of the CRC.

The technology can be implemented as a hardware solution or as acomputer program product comprising program code portions for performingthe method when the computer program product is run on a computingdevice. The computer program product may be stored on acomputer-readable recording medium that is for example in fixedassociation with or removable from the computing device.

A receiver is configured to be coupled by an adaptable communicationslink to a transmitter, wherein link adaptation is performed based on anestimate of the signal transmitted via the communications link to thereceiver. The receiver comprises a demodulator for demodulating thereceived signal, at least one processing component the furtherprocessing the demodulated signal, and a decoder for decoding thefurther processed signal. A first signal branch of the receiver iscoupled to a first node between the demodulator and the at least oneprocessing component.

The first branch includes a first estimating component for deriving afirst estimate for the signal quality that is to be utilized in a linkadaptation scheme. A second signal branch of the receiver is coupled toat least one of the processing component, the decoder and a second nodebetween a processing component and the decoder. The second signal branchis configured to transmit a first control signal that is indicative ofthe signal quality and that controls the link adaptation scheme. Theprocessing component preferably performs at least one of Rake combining,de-interleaving and one or more advanced receiver techniques likeinterference cancellation.

In the second signal branch a second estimating component can bearranged for deriving a second estimate for the signal quality based onwhich the first control signal may be generated. In addition to thefirst and the second signal branch a third signal branch may beprovided. The third signal branch can be coupled to a third nodearranged in a signal path after the decoder and may include anassessment unit that generates a second control signal for controllingthe link adaptation scheme.

According to a further aspect, a receiver demodulates a received signal,a decoder decodes the demodulated signal, a first signal branch iscoupled to a first node between the demodulator, and the decoder and asecond signal branch are coupled to the decoder or a second node in asignal path behind the decoder. The first signal branch includes a firstestimating component for deriving a first estimate for the signalquality that is to be utilized in a link adaptation scheme relating toat least one of adaptive coding and adaptive modulation. The secondsignal branch is configured to transmit a control signal which isindicative of the signal quality and controls the link adaptationscheme.

The receivers discussed above may be included in a mobile terminal likea UE. Alternatively or additionally, the receivers may be incorporatedin a non-mobile device like a BS.

According to still a further aspect, a wireless communications systemincludes a transmitter, a receiver and an adaptable communications linkbetween the transmitter and the receiver. The system comprises on areceiver side a demodulator for demodulating the transmitted signal, atleast one processing component for further processing the demodulatedsignal, and a decoder for decoding the further processed signal. Thesystem further comprises a first control loop stretching between thetransmitter and the receiver, the first control loop including a firstnode arranged between the demodulator and the at least one processingcomponent and further including a first estimating component forderiving a first estimate for the signal quality that is to be utilizedin a link adaptation scheme. The estimating component may be part of thetransmitter or of the receiver. The system further comprises a controlbranch including at least one of the processing component, the decoderand a second node between the processing component and the decoder. Thecontrol branch is configured to transmit a first control signal. Thefirst control signal is indicative of the signal quality and controlsthe link adaptation scheme.

A second control loop can be provided that includes the decoder or athird node arranged in a signal path after the decoder. The secondcontrol loop may additionally comprise an assessment unit for generatinga second control signal for controlling the link adaptation scheme orfor triggering re-transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a WCDMA wireless communicationssystem;

FIG. 2 is a schematic block diagram of a prior art link adaptationmechanism based on power control;

FIG. 3 is a first example embodiment of a link adaptation mechanismbased on power control;

FIG. 4 is a second example embodiment of a link adaptation mechanismbased on power control;

FIG. 5 is a third example embodiment of a link adaptation mechanismbased on power control;

FIG. 6 is a schematic block diagram of a prior art link adaptationmechanism based on adaptive coding and modulation;

FIG. 7 is a schematic block diagram of a fourth example embodiment basedon adaptive coding and modulation; and

FIG. 8 is a schematic block diagram of a fifth example embodiment basedon adaptive coding and modulation.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as particularembodiments, circuits, signal formats etc. in order to provide athorough understanding of the present invention. It will be apparent toone skilled in the art that the present invention may be practiced inother embodiments that depart from these specific details. Inparticular, while the different embodiments are described herein belowincorporated in a WCDMA system, the present invention is not limited tosuch an implementation, but for example can be utilized in anytransmission environment that requires link adaptation. Moreover, thoseskilled in the art will appreciate that the functions explained hereinbelow may be implemented using individual hardware circuitry, usingsoftware functioning in conjunction with a programmed microprocessor orgeneral purpose computer, using an application specific integratedcircuit (ASIC), and/or using one or more digital signal processors(DSPs).

FIG. 1 shows a wireless communications system 10 according to the WCDMAstandard. As has been mentioned before, the system 10 includes an RNC12, a BS 14, a first UE communicating with the BS 14 on DCH and a secondUE 18 receiving information from the BS 14 on HS-DSCH.

In FIG. 3 a schematic block diagram of a UE receiver 20 according to afirst example embodiment as implemented in the UE 16 depicted in FIG. 1is shown. The receiver 20 of FIG. 3 is configured to communicate via anadaptable communications link 22 with a transmitter in the form of theBS 14 depicted in FIG. 1. In the present embodiment the adaptablecommunications link 22 is the power-controlled DCH.

The receiver 20 of FIG. 3 comprises a receiver path 24 with ademodulator 26 for demodulating a received signal, a processingcomponent 28 for performing the processing operation of Rake combining,a further processing component 29 for performing interferencecancellation, and a decoder 30 which additionally performsdeinterleaving. It should be noted that interference cancellation neednot necessarily be performed immediately after Rake combining. It couldalternatively be performed after deinterleaving and prior to decoding.

The receiver 20 further comprises three signal branches 30, 32, 34. Afirst signal branch 30 is coupled to a node 40 between the demodulator26 and the processing component 28. The first signal branch 30 includesa first estimating component 42 that is configured to determine a firstquality estimate like a first SIR related value (e.g. the SIR value, aparameter required to determine the SIR value or a parameter derivedfrom the SIR value) on the basis of an output signal of the demodulator26. Alternatively, the first signal branch 30 could be coupled betweenthe processing component 28 for Rake combining and the processingcomponent 29 for interference cancellation.

A second signal branch 32 is coupled to a second node 44 between theprocessing component 29 for interference cancellation and the decoder30. The second signal branch 32 includes a second estimating component46 that determines a second quality estimate (e.g. a second SIR relatedvalue) on the basis of an output signal of the processing component 29,i.e. on the basis of a demodulated signal that has been subjected to theadvanced receiver techniques of Rake combining and interferencecancellation.

A third signal branch 34 is coupled to a third node 50 which is locatedin the receiver path 24 behind the decoder 30. The third signal branch34 includes a component 52 that evaluates a parameter which isindicative of the quality of the decoded signal. For example, the biterror rate (BER) or the frame error rate (FER) allow a reliableassessment of the signal quality. In the embodiment depicted in FIG. 3,a frame reliability indicator, namely the CRC check result obtained as aresult of decoding a particular user data frame, is assessed todetermine information relating to the quality of the decoded signal. Tothat end, the component 52 is configured as a CRC checker.

The receiver 20 of FIG. 3 further comprises two components 54, 56 thatallow to implement and control the specific link adaptation mechanism ofpower control used in the first embodiment. More specifically, thereceiver 20 includes a link adaptation unit 54 and a link adaptationcontroller 56. The link adaptation unit 54 is located in both the firstsignal branch 30 and the second signal branch 32. It may optionally alsobe included in the third signal branch 34. The link adaptationcontroller 56 is included in the third signal branch 34 only.

Both the link adaptation unit 54 and the link adaptation controller 56are configured to communicate on uplink with the BS 14 or, via the BS14, with the RNC 12 shown in FIG. 1. As becomes apparent from FIGS. 1and 3, the three signal branches 30, 32, 34 are part of differentcontrol loops that stretch between the receiver 20 of the UE 16 on theone hand and at least one of the BS 14 and the RNC on the other hand andthat include the adaptable communications link 22 on downlink as well asa plurality of control links 60 that will be discussed in more detailbelow.

Now the link adaptation mechanism performed during operation of thereceiver 20 depicted in FIG. 3 will be explained.

A signal received by the receiver 20 via the communications link 22 isdemodulated by the demodulator 26. Additionally, de-spreading in eachRake finger can be performed either in the demodulator 26 or in asubsequent processing component. The demodulated signal is input to boththe processing component 28 included in the receiver path 24 and thefirst estimating component 42 included in the first signal branch 30.Based on the demodulated input signal the first estimating component 42derives a first signal quality estimate that is fed to the linkadaptation unit 54.

The link adaptation unit 54 can implement various power control schemes.According to a first power control scheme, the adaptation unit 54includes a mapping mechanism for mapping the first signal estimatereceived from the first estimating component 42 on a signal qualityparameter that constitutes or can be translated into an adaptationsignal in the form of a power control command. This power controlcommand is then transmitted via one of the control links 60 on uplink tothe BS. In accordance with the received adaptation signal the BScontrols transmit power on the downlink communications link 22. Thus, afast power control loop may be established because the received signalis input into the first estimation component 42 with a comparatively lowprocessing delay. However, since the first signal quality estimate hasbeen generated by the first estimating component 42 on the basis of areceived signal that has only slightly been processed, the firstestimate of the signal quality (here a first SIR related value) is notvery accurate.

According to a second power control scheme that can be implemented bythe link adaptation unit 54, the first signal quality estimate in theform of the first SIR related value is compared with a target valuereceived via one of the control links 60 and via the BS from the RNC. Ifthe first SIR related value received from the first estimating unit 42is higher than the target value, a power control command is generatedthat commands the BS to lower the transmit power on the communicationslink 22. If the estimated first SIR related value is too low, anadaptation signal in the form of a power up command is sent to the BS.

As has been mentioned above, the demodulated signal is not only input tothe first estimating component 42 but simultaneously to the processingcomponent 28 that performs Rake combination. The Rake combined signal isthen subjected to interference cancellation. Interference cancellationconstitutes an advanced receiver technique that allows to reduce thetransmit power on the communications link 22 and thus enhances networkcapacity. Due to the complex mechanisms involved in interferencecancellation, the processing component 29 is associated with aconsiderable processing delay.

The output signal of the processing component 29 is fed to both thedecoder 30 and the second estimating component 56 in the second signalbranch 32. The second estimating component 46 assesses the signalreceived from the processing component 29 and generates a second asignal quality estimate in the form of a second SIR related value. Sincethis assessment is performed on the basis of a signal that has beendemodulated, Rake combined and subjected to interference cancellation,the accuracy of the second signal quality estimate is much higher thanthe accuracy of the first signal quality estimate generated by the firstestimation component 42. However, the second signal quality estimate isgenerated with a significantly higher processing delay.

The second signal quality estimate is output by the second estimationcomponent 46 and fed to the link adaptation unit 54. In the linkadaptation unit 54 the second signal quality estimate is used to adjustthe mapping rule for the first signal quality estimate.

If the link adaptation unit 54 implements the link adaptation schemeassociated with a target value, the second estimate for the SIR relatedvalue received from the second estimating component 46 may be used tochange the target value appropriately. For example in the case thesecond signal quality estimate (estimated second SIR related value) ishigher than the first signal quality estimate (estimated first for theSIR related value), the link adaption unit 54 may control the linkadaptation scheme such that the target value is lowered and vice versa.

Thus, the output signal of the second estimating component 46 is used tocontrol the link adaptation scheme implemented by the link adaptationunit 54. It can be seen that the fast link adaptation loop includes atwo-step signal quality estimation using a less accurate first signalquality estimate that is available with low processing delay and a moreaccurate second signal quality estimate that is obtained with a higherprocessing delay. In sum a fast and accurate signal quality estimationis achieved. It should be noted here that in principle the linkadaptation unit 54 could also be moved from the receiver 20 to the basestation 14 of FIG. 1.

In addition to the fast link adaptation loop described above an outerpower control loop is provided. The outer power control loop includesthe third signal branch 34 with the CRC checker 52 and the linkadaptation controller 56 and operates as follows. The CRC obtained as aresult of decoding of a particular user data frame is checked by the CRCchecker 52 and a corresponding check result is output as a frame qualityindicator to the link adaptation controller 56. The link adaptationcontroller 56 assesses the frame quality indicator and generates acontrol signal for controlling the link adaptation scheme. The linkadaptation scheme might be controlled either directly, i.e. via a directlink between the link adaptation controller 56 and the link adaptationunit 54 (dashed line), or indirectly via the BS and the RNC. In the caseof an indirect control the link adaptation controller 56 sends anadaptation control signal via one of the control links 60 and via the BSto the RNC and the RNC controls the link adaptation unit 54, which mayeither be part of the receiver 20 or of the BS as has been mentionedabove. In principle the link adaptation controller 56 may also be movedto the RNC or the BS.

Depending on the outcome of the assessment that is performed within thelink adaptation controller 56, the link adaptation scheme is controlled.Should for example the CRC check result indicate that the transmissionquality is changing, the mapping mechanism or the target value appliedby the link adaptation unit 54 may be changed upon receipt of acorresponding control signal from the link adaptation controller 56. Thelink adaptation controller 56 thus performs a similar task like thesecond estimating component 46. However, while the task of the secondestimating component 46 is based on a mere estimate of the signalquality, the task of the link adaptation controller 56 is based on astatistics of a plurality of “hard” CRC check results.

While the control of the link adaptation scheme by the link adaptationcontroller 56 is thus more accurate than the corresponding control bythe second estimating component 46, the control by the second estimatingcomponent 46 is associated with a much lower processing delay. This isdue to the fact that the second signal branch 32 including the secondestimating component 46 taps the receiver path 24 prior tode-interleaving and decoding, whereas the third signal branch 34including the link adaptation controller 56 taps the receiver path 24after de-interleaving and decoding. By means of the second estimatingunit 46 and the link adaptation controller 56 a two-step link adaptationscheme control is implemented.

It should additionally be noted that the embodiment depicted in FIG. 3allows better performance or link gain from the implementation ofadvanced receiver structures like interference cancellation componentsbecause the second estimating component 46 the signal enhancements aremodelled more accurately. Simultaneously, the first signal estimatingcomponent 42 allows a fast link adaptation that is not effected by theprocessing delay associated with interference cancellation.

In FIGS. 4 and 5, two further example embodiments of receivers 20 aredepicted. Since the embodiments are to a large extent similar to thefirst embodiment discussed above, only the differences to the firstembodiment will be explained in more detail.

Referring to FIG. 4 it can be seen that the first signal branch 30including the first estimating component 42 has been attached to thenode 44 between the processing component 29 and the decoder 30. Thesecond signal branch 32 has directly been attached to the decoder 30.Thus, the first signal quality estimate, i.e. the first SIR relatedvalue, is derived from the received signal after interferencecancellation and the second signal quality estimate is derived based onmetrics obtained during decoding.

In the third embodiment depicted in FIG. 5 the link adaptation unit 54is attached to the output of the decoder 30 via a fourth signal branch59. Thus, additional parameters for controlling the link adaptationscheme applied by the link adaptation unit 54 are provided.

In FIG. 7 a fourth example embodiment of a receiver 20 is shown. Thisreceiver 20 is part of the UE 18 which in FIG. 1 is attached to the BS14 on HS-DSCH.

The fourth example embodiment is based on the link adaptation mechanismof adaptive coding and modulation. As can be seen from FIG. 7, thereceiver 20 includes in a receiver path 24 a demodulator 62 thatadditionally performs Rake combining, a processing component 64performing interference cancellation, and a decoder 66 additionallyperforming de-interleaving. In a first signal branch 68 coupled to anode 70 between the decoder 66 and the processing component 64 anestimating component 72 for performing channel quality estimation isarranged. A second signal branch 74 is coupled to the decoder 66 andtransmits a first control signal, that has been generated based onmetrics information obtained during decoding, to the estimatingcomponent 72. A third signal branch 76 is coupled to a third node 80arranged in the receiver path 24 behind the decoder 66. An assessmentunit in the form of a CRC checker 82 is included in the third signalbranch.

Now the operation of the receiver 20 depicted in FIG. 7 will bedescribed in more detail.

A signal received by the receiver 20 via the adaptable communicationslink 22 is subjected to demodulation and Rake combination in thedemodulator 62 and to interference cancellation in the processing unit64. The estimating component 72 assesses the demodulated signal outputby the processing component 64 and derives an estimate for the signalquality in the form of a channel quality parameter. This channel qualityparameter is used in an uplink CQI signalling context to control themodulation scheme or data rate used on the communications link 22 (fastcontrol loop). The operations performed by the estimating component 72can be similar to the mapping mechanism or the comparison of an estimateof an SIR related value with a target value as explained above withreference to the receiver structure of the first embodiment.

A control signal in the form of metrics information obtained duringdecoding is fed via the second signal branch 74 to the estimatingcomponent 72 to control the channel quality estimation performed by theestimating component 72 and to thus control the link adaptation scheme.

As can be gathered from FIG. 7, an outer control loop including thethird signal branch 76 and the CRC checker 82 is additionally provided.The CRC checker 82 is configured to trigger re-transmission of aparticular frame in the case the CRC check for this frame has failed.

In FIG. 8 a fifth example embodiment of a receiver 20 is shown. Thefifth embodiment is similar to the fourth embodiment described abovewith reference to FIG. 7.

Again, the first signal branch 68 including the estimating component 72is coupled between the demodulator 90 (which in the fifth embodiment isintegral with the processing component for performing interferencecancellation) and the decoder 66. A second signal branch 92 is coupledfrom the node 80 behind the decoder 66 via the CRC checker 82 to theestimating component. A control signal in the form of the CRC checkresult may thus be input via the second signal branch 92 to theestimating component 72 controlling the link adaptation scheme, i.e. themodulation and code rate settings, by adjusting the parameters usedduring channel quality estimation.

While the present invention has been described with respect toparticular example embodiments, those skilled in the art will recognizethat the present invention is not limited to the specific embodimentsdescribed and illustrated herein. Therefore, while the present inventionhas been described in relation to its preferred example embodiments, itis to be understood that this disclosure is only illustrative.Accordingly, it is intended that the invention be limited only by thescope of the claims appended hereto.

1. A method of adapting a communications link between a transmitter anda receiver based on a quality estimate for a signal transmitted via thecommunications link, comprising: receiving and demodulating thetransmitted signal; a first control loop assessing the demodulatedsignal to derive a first estimate for the signal quality used in a linkadaptation scheme in which the first estimate is mapped on a signalquality parameter in accordance with a mapping rule or compared with atarget value; prior to decoding, further processing the demodulatedsignal, wherein based on at least one of the further processed,non-decoded signal and information obtained prior to conclusion ofdecoding a second control loop different from and slower than the firstcontrol loop derives a second different estimate for the signal qualityusing the further processed, non-decoded signal and uses the secondsignal quality estimate to control the link adaptation scheme byadjusting the mapping rule or changing the target value; a third controlloop different from and slower than the second control loop analyzingthe decoded signal to generate a third signal quality estimate differentfrom the first and second estimates and using the third signal qualityestimate to change the target value; and wherein the further processingincludes at least one of Rake combining, interference cancellation, andde-interleaving.
 2. The method of claim 1, wherein during or afterfurther processing the demodulated signal is assessed again to derive asecond estimate for the signal quality based on which the first controlsignal is generated.
 3. The method of claim 1, wherein at least one ofthe first control signal and the second estimate is generated based onmetrics information obtained during further processing or decoding. 4.The method of claim 1, wherein the link adaptation scheme defines anassociation between the first estimate and an adaptation signal to betransmitted by the receiver.
 5. The method of claim 4, wherein the firstcontrol signal changes the association between the first estimate andthe adaptation signal.
 6. The method of claim 1, wherein link adaptationincludes at least one of transmit power control, adaptive coding andadaptive modulation.
 7. The method of claim 1, wherein the third signalquality estimate is also used to control the link adaptation scheme. 8.A computer program product including a computer-readable storage mediumcomprising program code portions for performing the steps of claim 1when the computer program product is run on a computing device.
 9. Areceiver which is configured to be coupled via an adaptablecommunications link to a transmitter, wherein link adaptation isperformed based on a quality estimate of a signal transmitted via thecommunications link to the receiver, the receiver comprising: ademodulator for demodulating the received signal; an interferencecancellation component for further processing the demodulated signal; adecoder for decoding the interference canceled signal; a first signalbranch coupled to a first node between the demodulator and theinterference cancellation component, the first signal branch including afirst estimating component for deriving a first estimate for the signalquality that is to be utilized in a link adaptation scheme in which thefirst estimate is mapped on a signal quality parameter in accordancewith a mapping rule or compared with a target value; a second signalbranch configured to receive the interference canceled signal, and usinga second estimating component, derive a second signal quality estimateto be used in the link adaptation scheme along with the first signalquality estimate; and a third signal branch coupled to a third nodearranged in a signal path after the decoder, an assessment unit beingincluded in the third branch to generate a control signal forcontrolling the link adaptation scheme.
 10. The receiver of claim 9,further comprising a rake combiner for performing rake combining on thedemodulated signal prior to interference cancellation.
 11. A componentof a wireless communications system comprising the receiver of claim 9.12. A wireless communications system including a transmitter, a receiverand an adaptable communications link between the transmitter and thereceiver, wherein link adaptation is performed based on a qualityestimate of a signal transmitted via the communications link to thereceiver wherein the receiver includes the receiver of claim 9.